Heat control in vertical furnace by flue gas recirculation



Aug. 11, 1953 J. w. THROCKMORTON ET AL HEAT CONTROL IN VERTICAL FURNACE BY FLUE GAS RECIRCULATI ON Filed March 22, 1949 2 Sheets-Sheet l INVQVTORS JOHN w. THROCKMORTON 'JOHN s. WALLIS 44 1.;

ATTORNEY.

Aug. 11, 1953 HEAT CONTROL IN VERTICAL FURNACE BY FLUE GAS RECIRCULATION Filed March 22, 1949 J. w. THRoCKMoRfoN El AL 9 2 Sheets-Sheet 2 INVENTORS. JOHN-W. THROCKMORTON JOHN WALLIS ATTORNEZ Patented Aug. 11, 1953 UNITED STATES PATENT OFFICE HEAT CONTROL IN VERTICAL FURNACE BY FLUE GAS RECIRCULATION poration of Delaware Application March 22, 1949, Serial No. 82,874

This invention pertains to an upright furnace having vertical tubes forming a radiant section above the heat source, and an object of the invention is to provide means and method for controlling the heat in that radiant section.

In certain operations the tubes are filled with a catalyst so that the chemical reactions take place within the heating elements of a directfired furnace.

Temperature control within the radiant section for this operation is usually critical for various reasons:

(a) The operating temperatures may range from 700 F. to 1800 F. and in many cases the permissible temperature of the metal tubes becomes a limitation in the design of the furnace.

(b) The reaction through the catalyst beds in the tubes is of a variable nature, depending upon the charging stock, the type of catalyst used, and the end-products desired. For example, it may be advisable to bring the charge up to temperature as rapidly as possible, and as the reaction progresses, to reduce the heat intensity to a fraction of the average rate of heat absorption.

As the catalyst becomes poisoned, or less effective, at the end of the run, it may be desirable to change the heat intensity at different elevations in the furnace in order to have the least possible variation in the end-products of reaction.

The present invention meets the above critical conditions by recirculating the products of combustion within the radiant zone of the furnace.

Further and other objects and advantages will be apparent from the specification and claims,

and from the accompanying drawings which. illustrate what is now considered to be a preferred embodiment of the invention.

In the drawings:

Fig. 1 illustrates a sleeve, or hollow cylinder, above the burner;

Fig. 2 is a cross-section on line 2-2 of Fig. 1;

Fig. 3 illustrates a modification of the invention in which the sleeve above the burner is tapered in order to produce a Venturi effect. If desired, the angle of sleeve taper may be modified to vary the heat intensity on the tubes. A damper for controlling the rate of recirculation is provided;

Fig. 4 is a cross-section on line 4-4 of Fig. 3; and

Fig. 5 is an enlarged view, partly in section, showing the damper adjusting mechanism.

Figs. 1 and 2 illustrate a furnace having vertical tubes Ill filled with a catalyst, and a burner H2 in the middle of t e furn ce ifioor,

2 Claims. (0;. 23-277) Supported directly above the burner is a tubular metal sleev It which, as illustrated, is made in longitudinal sections for ease of replacement. The sleeve is supported above the floor by spaced apart fire bricks I8 resting on the floor. Above the sleeve I4 is a Well-known inverted conical baffle H. The radiant section of the furnace comprises substantially the entire interior of the furnace below a horizontal plane passing through and approximately half way up the cone H.

As a result of this construction, the hot gases from the burner rise through tube [4 into the radiant portion of the furnace While the burner, acting as an inspirator, recirculates some of the products of combustion downwardly outside tube 14, past the brick supports it into the bottom of the tube and then upwardly and outwardly again through the tube. The tube I 4 itself becomes heated and radiates heat to the tubes Ill at a temperature which is modified and controlled to the desired degree by the gas recirculation described.

The embodiment of Figs. 3, 4 and 5 also operates in the manner above described except that the cylindrical tube M is replaced by a conical tube which tapers upwardly and outwardly, thus producing a Venturi effect which accelerates the recirculation of the gases. Above the tube 26 is an inverted conical bafile similar to the baffle H. The radiant section of the furnace comprises substantially the entire interior of the furnace below a horizontal plane passing through and approximately half way up the cone 25.

In this modification the heat-absorbing tubes of the furnace are designated 22, the burner is 2 1, the support for tube 20 is fire bricks 26, the vertical tube around the burner is 28 and the furnace floor is 30.

In the throat of tube 20 is an annular band forming a damper 32 supported by threaded vertical rods 34 attached by brackets 36 to the lower rim of the damper (Fig. 5).

Rods are geared together by chain 38 and sprockets 48; therefore, when hand crank 42 is turned by the operator, the damper will move vertically to control the rate of recirculation of flue gases into and through tube 20.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

What is claimed is:

1. A vertical furnace comprising a radiant section having a hollow cylindrical bank of radiant heat absorbing tubes defining a vertical axis, a

burner at the bottom of said radiant section for discharging combustion products upwardly along said axis, said radiant section having a floor at the bottom thereof, an open ended recirculating tube located with its axis vertical and with its lower end spaced above said floor and adjacent to said burner, and a recirculation damper located at the lower end of said recirculating tube, said damper comprising an annular band movably supported adjacent the lower end of said recirculating tube, said band having a width at least equal to the space between said floor and the lower end of said recirculating tube, and means for moving said band vertically to regulate the size of the recirculation opening at the lower end of said recirculating tube in order to control the amount of recirculation which takes place.

2. A vertical furnace comprising a radiant section having a hollow cylindrical bank of radiant heat absorbing tubes defining a vertical axis, a burner at the bottom of said radiant section for discharging combustion products upwardly along said axis, said radiant section having a floor at the bottom thereof, a frusto-conical open ended recirculating tube located with its axis vertical and its small end down but spaced above said floor and adjacent said burner, and a recirculation damper located at the small end of said .for moving said band vertically to regulate the size of the recirculation opening at the small end of said tube in order to control and regulate the amount of recirculation which takes place.

JOHN W. THROCKMORTON. JOHN S. WALLIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 486,990 Tallmadge Nov. 29, 1892 700,664 Bryan May 20, 1902 1,546,038 Smith July 14, 1925 1,671,448 Plassmann May 29, 1928 1,729,763 De Florez Oct. 1, 1929 2,028,326 Hanks et a1 Jan. 21, 1936 ,174,663 Keller Oct. 3, 1939 2,276,527 Throckrnorton et a1. Mar. 17, 1942 2,294,254 Throckmorton et al. Aug. 25, 1942 2,424,765 McCollum July 29, 1947 2,430,344 Kemp Nov. 4, 1947 2,455,201 Wallis et a1. Nov. 30, 1948 2,500,499 Schuurman Mar. 14, 1950 

1. A VERTICAL FURNACE COMPRISING A RADIANT SECTION HAVING A HOLLOW CYLINDRICAL BANK OF RADIANT HEAT ABSORBING TUBES DEFINING A VERTICAL AXIS, A BURNER AT THE BOTTOM OF SAID RADIANT SECTION FOR DISCHARGING COMBUSTION PRODUCTS UPWARDLY ALONG SAID AXIS, SAID RADIANT SECTION HAVING A FLOOR AT THE BOTTOM THEREOF, AN OPEN ENDED RECIRCULATING TUBE LOCATED WITH ITS AXIS VERTICAL AND WITH ITS LOWER END SPACED ABOVE SAID FLOOR AND ADJACENT TO SAID BURNER, AND A RECIRCULATING DAMPER LOCATED AT THE LOWER END OF SAID RECIRCULATING TUBE, SAID DAMPER COMPRISING AN ANNULAR BAND MOVABLY SUPPORTED ADJACENT THE LOWER END OF SAID RECIRCULATING TUBE, SAID BAND HAVING A WIDTH AT LEAST EQUAL TO THE SPACE BETWEEN SAID FLOOR AND THE LOWER END OF SAID RECIRCULATING TUBE, AND MEANS FOR MOVING SAID BAND VERTICALLY TO REGULATE THE SIZE OF THE RECIRCULATION OPENING AT THE LOWER END OF SAID RECIRCULATING TUBE IN ORDER TO CONTROL THE AMOUNT OF RECIRCULATION WHICH TAKES PLACE. 